This invention relates generally to fiber optic face plates and more particularly concerns methods in which reactive liquid crystals and polymers can be utilized for fabrication of fiber optic faceplate equivalents.
Fiber optic faceplates (FOFPs) are useful in the construction of liquid crystal displays as disclosed in U.S. Pat. No. 5,442,467, filed on Mar. 21, 1994, by Silverstein et al., the subject matter of which is incorporated herein by reference. U.S. Pat. No. 5,442,467 discloses a direct-view rear-illuminated LCD device, comprising: a backlight source; a rear diffuser layer; a rear polarizer; a LC cell including a rear glass layer with addressing elements and indium tin oxide (ITO) transparent pixel electrodes, a LC layer having a top and bottom surface, and a front FOFP as a front containing element of the LC cell and being located directly in contact with the top surface of the liquid crystal layer; a mosaic array of color absorption filters either deposited on the front face of the FOFP or located on a separate but adjacent substrate; and a front polarizer or analyzer. Alternatively, the front polarizer or analyzer may be constructed from thin-film materials and located between the top or light exit surface of the LC layer and the bottom or light input surface of the FOFP.
An FOFP comprises an array of individual optical fibers which are fused together with an interstitial cladding material and then cut and polished to a desired thickness to form a plate. The creation of FOFPs with varying optical characteristics is well known in the art. The optical fibers are designed to transmit through total internal reflection light incident at controlled input or acceptance angles while rejecting or absorbing light incident at larger angles. Light entering the fibers at an entrance plane of the FOFP is collected over a wide acceptance angle .theta..sub.Max IN by use of a high numerical aperture (NA) FOFP and/or coupling to a boundary of low refractive index (e.g., air). Light exiting the optical fibers at an exit plane of the FOFP is made to diverge or exit over a relatively wide angle .theta..sub.Max OUT also by use of a high NA and/or the ultimate coupling to a low refractive index boundary. FOFPs with low NAs and/or coupling to relatively high refractive index materials (e.g., plastic, polyimide, or optical glass) restrict the light output exit angle, .theta..sub.Max OUT, of the exit plane of the FOFP and the light input acceptance angle, .theta..sub.Max IN, of the entrance plane of the FOFP, respectively.
These relations are illustrated in FIG. 1 for a typical optical fiber 10. Light beam 16 enters the optical fiber 10 within the acceptance cone 20 defined by an angle .theta..sub.max, which is measured from normal line N. and is totally internally reflected within a core 12 of the optical fiber 10 to propagate down the length of the optical fiber 10, essentially without loss. The normal N is perpendicular to an entrance plane 30 and an exit plane 32 of the optical fiber 10. If the relative index of material surrounding the optical fiber 10 at the entrance plane 30 and exit plane 32 surfaces (N.sub.o) is the same, then the light beam 16 will exit the optical fiber 10 at the same angle, in this example .theta..sub.max, which it entered. Light beam 18, which enters the optical fiber 10 outside of the acceptance cone 20 defined by .theta..sub.max is not fully guided through the length of the optical fiber 10 and "leaks" out of the optical fiber 10 into adjacent cladding material 14. Light beam 16 is a guided light beam while light beam 18 is an unguided light beam. An unguided or partially guided light beam may pass through the cladding material 14 and enter other fibers in a fiber-optic bundle or fused faceplate. However, unguided or partially guided light beams typically leak out of these fibers as well and continue to traverse the bundle or faceplate.
FIGS. 2 and 3 show the effects of varying the numerical aperture of the optical fiber 10. FIG. 2 shows the optical fiber 10 having a small numerical aperture and thus a smaller light acceptance cone 20. FIG. 3 shows the optical fiber 10 having a large numerical aperture and thus a larger light acceptance cone 20. Thus, the higher the numerical aperture of the fiber 10, the larger .theta..sub.max at the entrance plane 30 and the exit plane 32.
In general, light which enters the optical fiber 10 is rotated about a central axis of the optical fiber 10 as it propagates along the length of the optical fiber 10 as shown in FIG. 4. In this example the central axis of the optical fiber 10 happens to be coincident with the normal N used to measure the angle .theta..sub.max. Thus, light which enters at a given angle from the normal N to the fiber input surface exits the optical fiber 10 at the same exit angle, but at a rotated azimuthal position. This rotation is dependent on the number of reflections within the optical fiber 10 and also by the internal surfaces of the fibers. Skew rays typically undergo more rotation than meridional rays. For the application of FOFPs to LCDs, most of the illumination entering the fiber will be skew rays.
In FIG. 4, a light ray 24 and a light ray 26 can be seen entering the optical fiber 10 at the entrance plane 30 at an angle .theta..sub.max measured with respect to a normal N. Light ray 24 is parallel to light ray 26 and they enter the optical fiber at different points on the entrance plane 30. As each light ray 24, 26 exits at the output plane 32 of the optical fiber 10, it can be seen that each light ray 24, 26 exits at an angle .theta..sub.max but having undergone an azimuthal rotation angle .phi. around the central axis of the optical fiber 10.
As explained above, in fused fiber optic bundles and faceplates, both guided and unguided rays undergo azimuthal rotation. As shown in FIG. 4, the consequence of this rotation is that the optical fiber 10 averages about the azimuthal position all of the incoming light entering at a given declination angle such that the output consists of a hollow exit cone 22 with a solid angle of twice the entrance angle. In FIG. 4, because both illustrated incoming light rays 24, 26 enter the optical fiber 10 at an angle .theta..sub.max, the solid angle of the hollow exit cone 22 is 2.theta..sub.max. As the light emerging as a hollow exit cone 22 consists of an average about the azimuthal position, the transmitted light intensity is equal at all azimuthal angles. It is this property of azimuthal averaging that enables FOFPs to produce symmetrical viewing characteristics over wide angles when coupled to a LCD with inherent anisotropies in luminance and contrast.
FIG. 5 illustrates an FOFP 28 made of an array of individual optical fibers which are fused together with an interstitial cladding material and then cut and polished to a desired thickness to form a plate. The core 12 and cladding material 14 can be seen on the surface of the FOFP 28.
Therefore, any plate which has columnar features approximately in the direction of light propagation which are capable of total internal reflection, a controllable numeric aperture (NA) at input and output surfaces, rotational azimuthal averaging and translation of the object plane from a back surface of the plate to a front surface of the plate is the optical equivalent of a FOFP. These essential optical properties can be imparted to a range of materials, thus producing the FOFP optical equivalents. This application discusses a variety of monomer or polymer networks containing adjacent areas with differing refractive indices which result in a substrate containing a plurality of cylindrical features whose boundaries are defined by a discontinuity of refractive indices wherein the index of refraction within the cylindrical features is greater than the index of refraction at the boundaries and external to the cylindrical features.
Accordingly, it is the primary aim of the invention to produce substrates containing a plurality of cylindrical features whose boundaries are defined by a discontinuity of refractive indices wherein the index of refraction within the cylindrical features is greater than the index of refraction at the boundaries and external to the cylindrical features and wherein the substrates are fabricated out of reactive monomers or polymers.
Further advantages of the invention will become apparent as the following description proceeds.